The present invention relates to a production process of a dust core, and a dust core obtained using the production process.
For dust cores for electromagnetic parts, it is necessary and important to have a good handling property during their production step and have a mechanical strength high enough not to cause breakage during winding for making a coil. In consideration of such points, a technology of covering iron powders with an electrical insulating material is known in the field of dust cores. When iron powders are covered with an electrical insulating material, they are bonded to each other via the electrical insulating material so that a dust core available by using them can have an improved mechanical strength.
There has previously been disclosed a technology making use of a silicone resin having high heat resistance or a glassy compound available from phosphoric acid or the like as a material for preparing such an electrical insulating material (Japanese Patent No. 2710152).
The present applicants succeeded in providing a dust core having a high flux density, low iron loss, and high mechanical strength by forming, on the surface of an iron-based soft magnetic powder, a phosphate conversion coating film containing a specific element and a silicone resin film in this order and have already obtained a patent for it (Japanese Patent No. 4044591).
However, the demand for a dust core having a high performance has been rising recently compared with the application time of Japanese Patent No. 4044591. There is therefore an ever increasing demand for a dust core having a high flux density, low iron loss, and high mechanical strength.